The use of electronic cigarette (ecig), is gaining popularity among never and active smokers who are persuaded by intense ad campaigns that brands their use as a healthy alternative to cigarette smoke. In addition to the well- established noxious effects of cigarette smoke in the lungs, we have demonstrated that nano-sized carbon black particles, generated by incomplete combustion of tobacco, activate antigen presenting cells and promotes emphysema. Whether heated vaporized contents in ENDS (e.g. propylene glycol (PG), vegetable glycerol (VG) with or without nicotine) is a safe alternative to cigarette smoking in active or former smokers, remains unknown. We have developed a robust mouse model of conventional and electronic cigarette (ecig) exposure and made several novel discoveries that provide unique insights into the toxicology of ecig in the lungs. We have found that chronic inhalation of smoke, and ecig (with or without nicotine) elicits DNA adducts, and results cellular changes in the lungs. Further, when mice are transitioned from cigarette smoke to ecig, there is a significant suppression of lung innate mucosal immunity. In response to this RFA, we propose to use novel toxicology approaches to identify biomarkers, as well as test cardiovascular and respiratory health effects of ecig and its components to aid the FDA in formulating regulations applicable to the ENDS industry. To achieve our goal, we have designed a preclinical model that closely simulates human behavior to explore how transition from smoke to ecig could escalate their toxicity in the lungs. In addition, by tapping into an existing cohort of smokers who participate in neurocognitive behavior studies at BCM, conduct ancillary studies to identify novel biomarkers and determine whether ecig with and without nicotine alters innate immune function, and promote serum cumulative inflammatory potentials. To accomplish our goal, we will examine lung DNA adducts, metabolomics, lipidomics, and systemic innate immunity in mice exposed to chronic smoke and transitioned to ecig. We will also examine the role of ecig with and without nicotine on systemic immunity and metabolomics in human volunteers. We will test the following three specific aims: Aim 1: To examine the effects of components of ecig in DNA adduct formation using a preclinical model of transition from chronic smoke to ecig inhalation. Hypothesis: The ratio of PG/VG alters DNA adducts in the lungs. Aim 2: To identify toxic cellular responses to ecig using a preclinical model of transition from chronic smoke to ecig inhalation. Hypothesis: Chronic ecig exposure and/or transition to ecig in mice exposed to smoke alters endothelial and/or immune cell responses. Aim 3: To identify toxic cellular responses to ecig using a cohort of active smokers and ecig users. Hypothesis: Exposure to ecig alters endothelial and/or immune cell responses. Successful completion of the proposed preclinical and human translational studies provides relevant toxicological findings and inform the FDA how to regulate distribution, and marketing of ENDS products to protect public health.